01 - Preheat the oven to 400°F. Grease a 9x13-inch baking dish lightly with oil or cooking spray.
02 - Pat chicken breasts dry with paper towels. Season both sides generously with salt, pepper, and Italian seasoning. Arrange in a single layer in the prepared baking dish.
03 - In a medium bowl, whisk together heavy cream, grated Parmesan, minced garlic, and red pepper flakes until well combined.
04 - Pour the cream mixture evenly over the seasoned chicken. Scatter sun-dried tomatoes and chopped spinach around and between the chicken pieces. Sprinkle shredded mozzarella evenly over the top.
05 - Bake for 25-30 minutes, or until the chicken reaches an internal temperature of 165°F and the cheese is golden brown and bubbly.
06 - Remove from the oven and let the casserole rest for 5 minutes to allow the sauce to thicken slightly. Garnish with fresh chopped basil if desired and serve hot.